It is often essential to characterize biological particles by their size, surface condition, states of activation of any surface receptors, distribution, and the like. This information is useful in cell-based assays and other processes that rely upon those characteristics. Additionally, it is useful in certain diagnostic applications to detect known changes of the surface of a biological particle. Accordingly, it can be desirable to detect the surface and monitor changes to the surface in an efficient and accurate manner.
“Electrophoretic Quasi-Elastic Light Scattering” (EQELS) is one method for characterizing biological particles. This method uses electrophoresis that is dependent on the particle's surface charge density to identify and characterize suspended biological particles. EQELS uses cells placed in an electric field, where the surface charge of the particle will determine how that particle moves in the electric field. Monitoring the electrophoretic mobility of the cells provides information useful in distinguishing among different particles in the field. One can screen and optimize drug candidates which interact with the biological particles by comparing the spectra of the particles alone, or bound to the drug candidates.
Coulter counters can also be used to characterize biological particles. These devices are primarily used to count and size cells and other biological particles. The Coulter Counter works by drawing fluid containing the biological particle through a small opening located within a current between two electrodes. As the fluid is drawn through the opening, the biological particles flow through the current and measurably displace a portion of the current. The measurable displacement is translated to a pulse that is digitally processed by the Coulter Counter and translated to allow one to characterize the size and number of biological particles in the fluid.
Flow cytometry can also be used to characterize biological particles. Flow cytometry uses a beam of light, such as a laser, trained on a fluid to characterize, count and optionally sort particles in the fluid. The fluid is focused into a stream, and detectors at the intersection of the light and the fluid stream determine scatter—both forward and side. Additionally, a fluorescent detector may be present to detect fluorescent or fluorescently-tagged particles. One can determine various physical and chemical characteristics of each individual particle by analyzing the detected pattern.
These methods are useful in detecting and characterizing microparticles, including determining the number of particles, density within a fluid medium, size, and surface characteristics of the particle, confirming binding, or lack thereof, and the like. The microparticles are generally in the size of between 0.1 μm and 100 μm. However, developments in technology demand the characterization of smaller biological particles, including, but not limited to, nanoparticles.
The size of biological particles that can be analyzed using currently available technology is limited. Accordingly, there is a need for processes for characterizing biological particles that can detect biological particles of varying sizes, including particles smaller than microparticles, and which can characterize the detected particles with accuracy, quantify the particles and/or monitor the particles. The present invention provides such processes.